The present invention relates to methods and compositions for the controlled release of agents and components downhole in an oil recovery operation, and more particularly relates, in one embodiment, to emulsions for the controlled release of agents and components downhole.
Drilling fluids used in the drilling of subterranean oil and gas wells as well as other drilling fluid applications and drilling procedures are known. In rotary drilling there are a variety of functions and characteristics that are expected of drilling fluids, also known as drilling muds, or simply xe2x80x9cmudsxe2x80x9d. The drilling fluid is expected to carry cuttings up from beneath the bit, transport them up the annulus, and allow their separation at the surface while at the same time the rotary bit is cooled and cleaned. A drilling mud is also intended to reduce friction between the drill string and the sides of the hole while maintaining the stability of uncased sections of the borehole. The drilling fluid is formulated to prevent unwanted influxes of formation fluids from permeable rocks penetrated and also often to form a thin, low permeability filter cake which temporarily seals pores, other openings and formations penetrated by the bit. The drilling fluid may also be used to collect and interpret information available from drill cuttings, cores and electrical logs. It will be appreciated that within the scope of the claimed invention herein, the term xe2x80x9cdrilling fluidxe2x80x9d also encompasses xe2x80x9cdrill-in fluidsxe2x80x9d.
Drilling fluids are typically classified according to their base material. In water-based muds, solid particles are suspended in water or brine. Oil can be emulsified in the water. Nonetheless, the water is the continuous phase. Oil-based muds are the opposite. Solid particles are suspended in oil and water or brine is emulsified in the oil and therefore the oil is the continuous phase. Oil-based muds which are water-in-oil emulsions are also called invert emulsions.
It is apparent to those selecting or using a drilling fluid for oil and/or gas exploration that an essential component of a selected fluid is that it be properly balanced to achieve the necessary characteristics for the specific end application. Because the drilling fluids are called upon to do a number of tasks simultaneously, this desirable balance is not always easy to achieve.
It would be desirable if compositions and methods could be devised to aid and improve the ability of drilling fluids to accomplish these tasks by delivering agents and components downhole, which could be released controllably to accomplish one or more jobs.
Accordingly, it is an object of the present invention to provide a method and composition for delivering an agent downhole in a hydrocarbon recovery operation, particularly during a drilling and/or completion operation.
It is another object of the present invention to provide a method and composition for delivering an agent downhole where the agent is released at a controlled time and place.
In carrying out these and other objects of the invention, there is provided, in one form, a pumpable multiple phase composition, also called a multiple phase emulsion drilling or completion fluid, for carrying an agent having a first phase, a second phase, and a third phase. The first phase is suspended in the second phase to form a first pumpable emulsion, and next the first pumpable emulsion is dispersed in the third phase to form the final pumpable multiple phase composition. The pumpable multiple phase composition may be an oil phase-in-aqueous phase-in-oil phase emulsion, or an aqueous phase-in-oil phase-in-aqueous phase emulsion. The agent is present in the first phase.
Additionally, there is provided in one form, a method for releasing an agent downhole beginning by forming a first pumpable emulsion for carrying an agent. The first pumpable emulsion has a first phase containing the agent, and a second phase. The first phase is suspended in the second phase to form a first pumpable emulsion. The first pumpable emulsion may be an oil phase-in-aqueous phase emulsion, or an aqueous phase-in-oil phase emulsion, where the agent is present in the first phase or is the first phase. Next, the first pumpable emulsion is injected into a fluid which may be either a drilling fluid or a completion fluid, such that the external phase of the drilling or completion fluid is immiscible with the second phase of the first pumpable emulsion thereby forming a pumpable multiple phase composition (multiple emulsion). Finally, the pumpable multiple phase composition is broken downhole to release the agent. The pumpable multiple phase composition may be broken by shear, for example, by pumping through drill bit nozzles.
Pumpable multiple phase compositions (emulsions) are anticipated as being useful to organize a liquid phase to isolate one miscible phase from another. An oil-in-water emulsion could be used in an invert emulsion, hydrocarbon-based or ester-based or other water immiscible, non-aqueous-based system (forming an oil-in-water-in-oil system), while a water-in-oil emulsion could be used in an aqueous system (forming a water-in-oil-in-water system). In short, the multiple emulsion compositions of this invention and methods for their use may be applied to any two immiscible phases that form stable emulsions. The phases need not be xe2x80x9coilxe2x80x9d and xe2x80x9cwaterxe2x80x9d, although such phases are likely to be the most common implementation. One non-limiting example is the combination of a water soluble, relatively high molecular weight glycol that forms an emulsion with brine.
One important application of this kind of organization would be the controlled release of the internal phase contents, such as an agent within the innermost (first) phase. A non-limiting example of such an application would be the emulsion of, for instance, a polyglycol, potassium salt, aluminum salt, calcium salt, a silicate salt, chelate or other shale stabilizer, or an aqueous solution thereof, as a first, internal phase in a hydrocarbon or hydrophobic carrier (second phase) optionally containing an emulsifier and/or stabilizer, and then adding the emulsion to a water-based drilling fluid. The polyglycol, potassium salt, aluminum salt, etc. or other shale stabilizer, alone if liquid, or in solution, e.g., is isolated from the water in the external phase of a water-based drilling fluid. Dilution is prevented, suppressed, or delayed until the emulsion is broken intentionally. A likely area for breakage of the emulsion is the high shear environment of and below the drilling bit, where the shale stabilizer is released to the borehole and cuttings in concentrated form on a localized basis. While the invention does not contemplate, as a preferred embodiment, making the multiple emulsion so stable that it is not broken in a drilling fluid or completion fluid application, such stable multiple emulsions are anticipated and may find utility.
Of course, emulsifiers, viscosifiers, or other structural stabilizers may also be added to increase the mechanical stability of the first pumpable emulsion in some cases to delay release of the contents (agent).
In more detail, the agent to be delivered as the contents of the internal phase or the first phase, may be any conventional agent, including, but not necessarily limited to, a shale stabilizer, as noted above, a filtration control additive, viscosifier, suspending agent, dispersant, thinner, an anti-balling additive, a lubricant (particularly in the oil-in-water-in-oil multiple phase compositions), a wetting agent, a seepage control additive, a lost circulation additive, drilling enhancer, penetration rate enhancer, corrosion inhibitor, acid, base, buffer, scavenger, gelling agent, cross-linker, catalyst, and the like, and mixtures thereof. Specific useful shale stabilizers include, but are not necessarily limited to, polyglycols, potassium salts, aluminum salts, calcium salts, silicate salts, chelates, amines, alkanolamines, alkanolamides, amphoteric compounds, alone if liquid or in aqueous solutions, and mixtures thereof. Some other specific agents include, but are not limited to amines (failing quartz bonds in certain sands, corrosion inhibitors in clay based systems, shale stabilizers) and metal halides, e.g. aluminum and thorium halides. The term xe2x80x9cacidsxe2x80x9d in this context includes organic acids and inorganic acids. Such acids can be used to treat cement contamination. If appropriate or desirable, the agent may be in aqueous or hydrocarbon solution.
This first or internal phase should match that of the ultimate fluid in which the first pumpable emulsion is to be injected or added. That is, if the first pumpable emulsion is to be injected into an aqueous fluid, the first, internal phase should be aqueous; if the fluid is hydrophobic, the first, internal phase should be hydrophobic.
Of course, the second phase, which together with the first or internal phase forms the first pumpable emulsion, should be of the opposite type. It may be necessary or desirable to add emulsifiers, viscosifiers, stabilizers, and mixtures thereof as structural stabilizers to increase the mechanical stability of this first emulsion to aid in delaying release or breaking. In the context of this invention, emulsifiers should be understood to include, but are not limited to, surfactants and the like, and viscosifiers are understood to include, but are not limited to, gelling agents and the like. The emulsifiers and viscosifiers may be in liquid or solid (e.g. powder) form. Suitable emulsifiers include, but are not necessarily limited to, sorbitan fatty acid esters including sorbitan monooleate and sorbitan trioleate, glycerol fatty acid esters including mono- and/or dioleates, polyglycerol fatty acid esters, polyglycols, alkanolamines and alkanolamides such as ethoxylated amines, ethoxylated amides, ethoxylated alkanolamides, including non-ethoxylated ethanolamides and diethanolamides, and the like. Viscosifiers and gelling agents include, but are not necessarily limited to, polymers of ethylene, propylene, butylene, butadiene, styrene, vinyltoluene and various copolymers and terpolymers thereof, organophilic clays, aluminum soaps and alkoxides and other aluminum salts, alkaline earth soaps, lithium soaps, fumed silica and alumina and the like and mixtures thereof. Other suitable stabilizers include, but are not necessarily limited to, cholesterol and long chain oil soluble waxy alcohols, and the like. These structural stabilizers would usually be added directly to the second phase although they may be added to the third phase, if that is more convenient. In one non-limiting embodiment of the invention, the proportion of structural stabilizer based on the second phase ranges from about 0.1 to about 90 vol. %, preferably from about 1 to about 50 vol. %.
However, the pumpable multiple phase compositions of the invention (emulsions) are designed to be broken in a preferred embodiment. Indeed, they are desirably and rather controllably broken within a certain area of the borehole at a designated and relatively controlled time.
The preparation of the first pumpable emulsion would typically involve the mixing of the first phase with the second phase, where any emulsifier or structural stabilizer is preferably present in the second phase. The speed of stirring or mixing of the two phases would depend upon the size of the emulsified internal phase droplets desired, and the particular system used. It is expected that the size of the first phase droplets would range from about 0.01 to about 1000 microns or less, preferably from about 1 to about 100 microns or less, as non-limiting examples. In one embodiment of the invention, the first phase droplets would be as large as is practical. The proportion of first, internal phase to the overall first pumpable composition may range from about 90 to about 5 vol. % or less, preferably from about 60 to about 40 vol. % or less, and most preferably, 50 vol. % or less, as non-limiting examples. A lower threshold of 5 vol. % may be appropriate in some embodiments of the invention.
The formation of the first pumpable emulsion could be accomplished within an injection pump itself. This technique would be similar to in-line mixing the first, internal phase xe2x80x9con the flyxe2x80x9d with the second phase forming the first emulsion before it exits into the third phase finally forming the multiple emulsion in the mud system.
The first pumpable emulsion is then, in turn, suspended in the drilling and/or completion fluid which is the third phase. This third phase is generally to be miscible with the first phase and may contain an emulsifier to help disperse the first pumpable emulsion into suitable sized droplets. Conventional drilling and/or completion fluids may be used as the third phase. If the third phase is oil-based or a hydrocarbon, in a preferred embodiment, the hydrocarbon is a synthetic material, and, for instance, may include, but is not necessarily limited to, esters, iso-olefins, alpha-olefins, polyolefins, poly-alpha-olefins, paraffins, Fischer-Tropsch reaction products, and the like. The oil phase may be a mixture or blend of petroleum distillates and synthetic hydrocarbons. Suitable petroleum distillates include, but are not limited to, diesel oil, kerosene, mineral oils, food grade mineral oils, paraffinic oils, cycloparaffinic oils, aromatic oils, or n-paraffins, isoparaffins and similar hydrocarbons. Crude oil could be used in some cases. In the case where the second phase is an oil-based phase, it is anticipated that any of these hydrocarbons may be used.
In the case where the multiple phase composition is water-in-oil-in-water multiple emulsion, the aqueous phase may be brine. Careful adjustment of the internal phase salinity of brine multiple emulsions may be required (osmotic pressure gradient adjustment). Too much salt or too low an activity in a first aqueous phase may make the droplets unstable. However, this mechanism may be intentionally used to cause failure or rupture of the first pumpable emulsion droplets or capsules downhole. For example, the droplets could be designed to grow on the journey downhole and break at or near the desired zone.
It is expected that the size of the droplets of the first pumpable emulsion (first phase in second phase) in the third phase would range from about 10,000 to about 1 micron or less, preferably from about 5 to about 1,000 microns or less, as non-limiting examples. In one embodiment of the invention, the pumpable emulsion droplets would be as large as possible. The larger the first phase droplets in the first emulsion droplets, all things being equal, the easier it would be to break the multiple phase composition to release the agent from the first emulsion.
The proportion of the first pumpable emulsion to drilling and/or completion fluid (third phase) may range from about 0.5 to about 90 vol. %, alternatively from about 0.5 to about 40 vol. %, preferably from about 1 to about 10 vol. %, in another embodiment from about 1 to about 5 vol. %, and most preferably from about 2 to about 6 vol. %, as non-limiting examples, to make the overall pumpable multiple phase composition.
Conventional drilling and/or completion fluid additives may, of course, be employed, including, but not necessarily limited to, wetting agents, viscosifiers, suspending agents, weighting agents, shale stabilizers, filtration control additives, anti-balling additives, lubricants, seepage control additives, lost circulation additives, corrosion inhibitors, alkalinity control additives, thinners, dispersants, and the like. Indeed, the agents to be delivered by the multiple emulsion compositions and methods herein may also be present in the third phase.
The method of this invention may find particular usefulness in increasing the local concentration of an agent downhole after rupture of the first pumpable emulsion droplets while keeping the overall concentration of the agent in the drilling mud (including the entire multiple phase composition) low. For example, styrene-butadiene rubber (SBR), useful as a viscosifier and/or filtration control additive, could be the agent in the first phase of the first pumpable emulsion and be in relatively low concentrations overall. However, once the first pumpable emulsion droplets are broken or failed, the local concentration of SBR at the droplet failure zone would be relatively increased.
Using the pumpable emulsion composition of the invention is straightforward and requires no special equipment. The first pumpable emulsion is injected into a fluid that is pumped downhole. The fluid may be a drilling fluid, drill-in fluid, a completion fluid, or the like. In a preferred embodiment of the invention, the fluid is a drilling fluid or drill-in fluid. A number of mechanisms could be used to break the pumpable multiple phase composition at a particular time, including, but not limited to, input of energy, including but not limited to, an increase in temperature, increase in pressure, increase in shear stress or shear rate, mechanical action (such as a rotating drill bit or drill string), change in pH, change in electrical potential, solvent thinning, presence of a chemical agent, presence of a catalyst, change in magnetic flux, and the like. A non-limiting, but preferred method is breaking the multiple phase composition by subjecting it to a high shear environment, in particular the fluid stream exiting a nozzle impinging on the borehole such as below a bit or opposite a reamer or hole opener. In a preferred method of the invention, the multiple phase emulsion is broken within a required period of time, and within a required physical volume. In one embodiment, if the agent being delivered was a shale stabilizer, the shale stabilizer could be delivered essentially instantaneously to the borehole and cuttings in a concentrated form on a localized basis.
It will also be understood that more than one agent may be delivered downhole, and that the two or more agents may interact or react with each other to provide a beneficial effect. For example, crosslinkers could be transported in first water-in-oil emulsion in the same aqueous third phase as a second water-in-oil emulsion containing the agent to be cross-linked. Alternatively, two separate internal phases which react on contact could be delivered in the same first emulsion added to the third phase such as an aqueous cross-linker and aqueous polymer solution could both be transported in the same first emulsion and added to a water-based mud. Indeed, one reactant could be present in the third phase and another reactant could be present in the first phase and the reaction could occur when the boundary of the second phase (first pumpable emulsion) is broken.
The agent may also be a polymer serving any of the stated functions, or a monomer to be polymerized or in the course of being polymerized to such a polymer.
Further, the multiple phase compositions of this invention are not limited to utility in downhole applications, but could be used to deliver and transport agents along a pipeline or other conduit, such as agents to prevent blockages (e.g. asphaltenes, hydrates, etc.) in a subsea pipeline or the like, or other agents. Any of the agents previously mentioned may be used in this way, and suitable agents may additionally include, but are not limited to, hydrate inhibitors, asphaltene inhibitors, scale inhibitors, etc.